Ask Jimmy and the Bug

art by Dean Stanton, text by Ellen Braaf

Hey Bug! Jaal M. from Costa Rica asks: “If the clouds are made of water why are they white?”

What a cirrus question!

Clouds are white for the same reason the sky is blue—because of what happens to sunlight.
Sunlight is really a combination of different lights in all the colors of a rainbow—red, orange, yellow,
green, blue, indigo, and violet. We can see these colors if the light gets broken up, for example, by a prism.
But we see all these colors together as white light.

On its way to Earth, sunlight runs into all kinds of little particles, including air molecules, dust, pollution, water droplets, and ice crystals.
These particles scatter the light in different directions, but the different types of particles don't scatter light the same way.

The tiny molecules that make up the Earth's atmosphere scatter the blue light best. Most
of the sun's rays reach the ground as white light, but some of the blue light gets scattered
in all directions in the sky, so no matter where you look the sky appears blue. The large water droplets or ice
crystals that make up clouds scatter all the colors of light equally, so clouds appear white.

Jimmy tries to take a cloud home in a bottle.

Activity

What color is Earth's atmosphere? Why is it this color?[anno: Earth's atmosphere is blue. The atmosphere is blue because sunlight hits particles in Earth's atmosphere. Those particles scatter more blue light than other colors of light, so the atmosphere appears blue.]

Most clouds are white, but storm clouds are often dark and gray. Why do you think storm clouds are gray?[anno: Answers may vary but could include that storm clouds are gray because they have more water in them than regular clouds. Students might also answer that storm clouds have debris, such as dust, in them.]

Imagine you are standing outside during a summer day. The Sun is high in the sky, and then a cloud passes in front of the Sun. What happens to the light? Does it become as dark as night? Why not? Write a sentence or two for your answer.[anno: Answers may vary but could include that the sky does not become as dark as night because most of the sunlight still goes through the cloud, and there is light still hitting Earth around the cloud.]